The vehicle simulator art, and in particular the aircraft simulator art, has reached a state of impressive sophistication. This is evident, for example, in the dependent disciplines of motion systems, auxiliary haptic sensory cueing devices (e.g., G-Seats), and faithful cockpit environmental reproduction. Consequently, flight simulators have in the recent path been utilized in connection with such demanding applications as tactical fighter pilot air-to-air combat training.
A related dependent discipline, also sophisticated but in need of improvement, is the visual simulation art. While enormous strides have been taken in the area of image generation, particularly in digital image generation techniques, display systems have fallen short in viewing angle characteristics.
The most typical such simulator visual system utilizes a high resolution CRT and collimating optics. However, in order to meet brightness and resolution requirements, the total displayed field of view permitted by a single CRT is limited to typically 48.degree. horizontal and 38.degree. vertical. Prior attempts to extend this field of view to accommodate the demands of tactical training applications utilized the technique of providing a mosaic of CRT display packages. It has been discovered, however, that this represents a less than totally satisfactory solution, as it inevitably results in compromises arising from optical considerations and mechanical interference between adjacent displays manifested as gaps in the field of view. Such a system also presents a limited exit pupil, requiring low intensity lighting in the simulator cockpit. Further, the maintenance problems associated with matching and aligning such a complex of separate displays are formidable.
TV projectors have been used with some success, particularly in connection with "dome" type displays in which the display screen takes the form of a spherical dome surrounding the simulator cockpit. Perhaps the most suitable such projector available heretofore has been the light valve projector. A commercially available 1,000 lines version was especially developed, in fact for the flight simulation industry. Although visual display systems incorporating this projector are free from some of the problems inherent in the CRT/collimating optics approach, they still do not represent a fully acceptable answer to the wide angle display requirement. Currently available light valve projectors exhibit, for example, vignetting and edge distortion that makes it impossible to achieve a continuous quality image. In addition, such systems require that three or more projectors be located on a single simulator fuselage. Presently in development for display applications is the liquid crystal light valve. While this possesses the potential for significant improvements both in light output and image uniformity, devices demonstrated thus far have exhibited lag and poor contrast ratio. Further, for wide angle display applications, multiple displays, with their attendant difficulties as previously discussed, would still be required.
The most promising approach to the wide angle display problem appears to be in the use of laser projectors. In such systes, a laser beam is generated and intensity modulated with video information, typically by means of an acoustooptic cell, and then scanned in the pattern of a raster onto a display surface, such as a screen. Such systems provide much improved brightness over previous systems, due to the high intensity inherent in laser light. In addition, the mechanical scanning devices employed in such systems permit a continuous wide angle view to be scanned onto a display surface. For example, U.S. Pat. No. 3,992,718 entitled "Color Panoramic Laser Projector" which issued Nov. 16, 1976 to Carl R. Driskell, disclosed a laser projector display system which provides a continuous 360.degree. image, completely surrounding the viewer.
However, the "brute force" approach of simply stretching the scanning window to the desired wide angle size revives resolution problems. A field of view of even 175.degree. by 75.degree., for example, if it is to provide the resolution which is demanded in modern flight simulator applications, requires that the system operate with a bandwidth of approximately 100 MHz. This places severe design demands on the modulator system, and poses the further problem of incompatibility with the digital image generation system employed in the simulation art.
The present invention solves these problems and, by virtue of a novel and ingenius optical scheme which permits, for example, a 140.degree..times.48.degree. field of view scanned laser image possessing requisite resolution, to be generated by means of a system having a bandwidth of less than 40 MHz.